Al Ewing, the author of the soon to be Loki: Agent of Asgard confirmed on Tumblr today that he will be exploring the Norse villain's fluid sexuality.
"lady-loki-odinson: Do you think COMIC Loki is Bisexual ? Loki is the Norse IS Bisexual . [Loki is a bisexual, shape-shifting norse God].
Ewing: Yes, Loki is bi and I'll be touching on that. He'll shift between genders occasionally as well."

Good on Ewing for being accurate to the mythology, but expect to see an increase in Tom Hiddleston slash fic in the coming months.